A technique to extract and visualize vortices in a fluid space is preferable for determining the behavior of a fluid in various fields including, for example, the behavior of wind around wings of an airplane, water flows around screws of a ship, and air flowing through the human trachea.
Various techniques to extract vortices have been proposed in order to realize visualization of the vortices. A major challenge to the visualization technique is to handle a very large amount of data in order to extract vortices accurately. Thus, a high-speed large-sized arithmetic machine that handles a large amount of data at a high speed is preferably used. The amount of calculation for vortex extraction is preferably reduced. However, a greater challenge is the level of the visualization. In association with a large amount of data used for the calculation for the vertex extraction, a large amount of data is used to express extracted vortices. Thus, the visualization process is difficult to achieve unless a computer is used which is specified so as to demonstrate the same level of performance as that of the computer used for the vortex extraction. That is, visualization with an insufficiently specified computer leads to slow responses to operations such as rotation, movement, enlargement, and reduction of displayed vortices. Thus, obtaining preferable display is difficult. Furthermore, the vortices vary momentarily. Hence, temporal variations in vortices are preferably determined in order to know the behavior of the vortices. However, owing to the large amount of data used for the vortex extraction, visualizing temporal variations in vortices is difficult.
When the data is decimated for visualization in order to achieve a high-speed visualization process, important phenomena may be lost by the decimation and fail to be displayed despite having spent the calculation cost to accurately extract the vortex. Thus, such phenomena may be missed.
The followings are documents related to the vortex extraction, documents disclosing examples of a region splitting method for allowing a large amount of data to be handled, and documents to be refer to in the description provided later.    (1) Japanese Laid-Open Patent Publication No. 2001-132700    (2) Japanese Laid-Open Patent Publication No. 2005-309999    (3) Japanese Laid-Open Patent Publication No. 2000-339297    (4) D. Sujudi, R. Haimes, IDENTIFICATION OF SWIRLING FLOW IN 3-D VECTOR FIELDS, Paper of American Institute of Aeronautics and Astronautics, 1995    (5) T. Weinkauf, Cores of Swirling Particle Motion in Unsteady Flows, Paper of IEEE, 2007    (6) On the identification of a vortex, Jinhee Jeong and Fazle Hussain, Jaurnal of fluid mechanics, vol. 285, pp 64-94, 1995    (7) Marching cubes: A high resolution 3 D surface construction algorithm, William E. Lorensen, Harvey E. Cline, Proceedings of the 14th annual conference on Computer graphics and interactive techniques, Pages: 163-169, 1987